1. Field of the Invention
This invention relates to anchors for refractory linings in process equipment, and more particularly to improved anchors which are less subject to stress cracking than previously available anchors.
2. The Prior Art
Refractory linings have been used for many years in process vessels, reactors, conduits, furnaces and the like to provide thermal insulation, and in environments such as fluidized catalytic reactors or regenerators or stacks to provide resistance to abrasion or erosion. Such linings can serve not only to thermally insulate a shell or other surface but also to prolong its service life by shielding it from erosion by abrasion. In fluid catalytic cracking units for petroleum hydrocarbons, quite high fluid velocities which may be on the order of 50 to 70 ft/second occur, and the abrasive effect of entrained cracking catalyst is very pronounced. Moreover, high temperatures are involved. For example, in the regenerator the temperature of gases exiting through the cyclones may be on the order to 1250.degree.-1350.degree. F. and in the reactor the temperature may be 800.degree.-900.degree. F. Accordingly, the usual practice has been to line all vessels, conduits and cyclone separators through which fluid with entrained catalyst flows with a refractory lining to protect the metal surfaces and to provide thermal insulation. To retain the refractory, which may be a refractory cement, a concrete cement-aggregate mixture, or a reinforced cement or concrete, on the metal surface, various anchoring arrangements have been employed.
Heretofore, a preferred anchorage arrangement which also provided erosion protection was the use of hexagonal steel grating which was welded to the vessel or conduit wall. The grating had the same depth as the refractory lining to be applied, and the refractory was deposited in the hexagonal spaces defined by the grating. Thus, the grating provided the desired erosion resistance for the refractory by projecting to the exposed surface of the refractory. The disadvantages of hexagonal grating are its relatively high cost, lack of flexibility, which makes it difficult or impossible to apply to curved surfaces, its tendency to separate from the vessel or conduit wall over relatively large areas when welds fail, and its unsuitability for use with fiber reinforced refractories or with refractory concretes containing coarse aggregate particles.
In situations where hexagonal grating is not suitable, weldable studs have been proposed. Such studs are suitable for use with fiber reinforced refractory or with refractory concrete, but do not provide significant erosion protection for the refractory.
In recent years, an anchor commonly called an S-bar anchor has been developed. U.S. Pat. No. 4,479,337 to Crowley, contains a comprehensive description of S-bar anchors and their use. S-bar anchors of the type disclosed therein have met with considerable success, and have been widely used. However, the S-bar anchors as described therein have had certain problems in service, and there has been a need for an improved S-bar anchor which is not subject to the problems of prior art S-bar anchors.